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Chapter 13

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Natural Science
NATS 1880
Paul Delaney

13.1 The Challenge of Interstellar Travel Why is interstellar travel so difficult?  The large distances between stars, the speed of light being the fastest speed, and enormous amount of energy required to accelerate any ship to high speed are three difficulties with interstellar space. Spacecraft bound for the stars  At current speeds it takes 100,000 years to reach the closest stars.  The pioneer carries a plaque  The voyager carries a gold-coated copper record The cosmic speed limit  According to Einstein’s Theory of relativity it is not possible to travel at or faster than the speed of light. Energy Issues  The energy required to accelerate an interstellar spaceship depends on its mass 2 and final velocity (mv )  The energy required to accelerate that Titanic to 10% of speed of light, will require 100X the Earth’s annual energy usage. Could we travel to star with existing rockets? Development of the rocket  Chemical rockets work on the principle of Newton’s third law of motion  Chemical rockets are the most common type of spacecraft Rocket Equation  The rocket equation relates final velocity to velocity of exhaust gases and ratio of the mass of rocket with all its fuel to mass of rocket after fuel has been consumed  The mass ratio of a rocket is define by mass of fully fueled rocket divided by mass of the rocket after fuel is burned  The earths escape velocity is the minimum velocity required for an object to escape the Earth’s gravity.  A mass ratio of 39 is required to leave Earth’s gravity  In order to get payload into space, we must use multiple rocket stages  The maximum terminal velocity we can accelerate a chemical rocket is 0.1% speed of light. 13.2 Designing Spacecraft for Interstellar Travel How might we build interstellar spacecraft with “conventional” technology? Nuclear Rockets  Nuclear FIZZION is the process in which large nuclei break up into smaller nuclei o It is more human so only 0.07% efficient  Nuclear FUSEion is the process in which smaller nuclei combine to form larger nuclei  The resultant helium is less massive than original four because energy is lost o It is natural so 0.7% efficient  The maximum speed we can accelerate a nuclear rocket is 10% speed of light. Projects  Project Rover in 1950’s developed nuclear fission reactors for rockets.  Project Orion in Los Alamos developed design for ship powered by H-bombs  Project Daedalus designed by British Interplanetary Society in 1970 was propelled by nuclear fusion reactors. Io
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